Vaccine effectiveness, how it multiplies and more

A health worker prepares an injection of the Moderna booster vaccine. Image: Leon Neal/WPA Pool (Getty Images)

The Covid-19 pandemic is reviving again in the US and elsewhere, and while we now have far more resources against the viral disease than we did last winter, namely a full armada of preventive vaccines and Treatments to be debuted soon— the rise of the Omicron variant around Thanksgiving threw a spanner in the works. Even if Omicron hadn’t come into the picture, the US would still face an increase in Covid-19 cases, deaths and hospitalizations.

Below is a summary of some of the most recent studies on Omicron and its risks. It is important to note that many of these studies are still preliminary and may not have undergone peer review, so their conclusions should be viewed with extra caution. It takes time and a base of evidence to be sure of anything.

A rapidly spreading and growing threat

Omicron has made scientists nervous because of the unique mix of mutations that make it look and behave differently from the original coronavirus, as well as from previous variants. It is theorized that these mutations could make the virus more easily transmitted between people and better evade the immune systems of people who were vaccinated or infected in the past. And we’re now starting to see data that supports those theories.

This week, a preliminary lab study from researchers in Hong Kong found it that Omicron can infect and multiply the cells of our bronchus (the two tubes that carry air from the windpipe to the lungs) much faster than the Delta variant could – up to 70 times faster. This voracious speed could explain why cases of Omicron have appeared in the real world: spread much faster than the standard covid outbreak, even among largely vaccinated populations.

But there may be a silver lining here: The same study found that Omicron didn’t replicate as quickly as Delta in the cells of the lung. That could possibly explain why some data suggests that Omicron causes milder disease than previous variants. But covid-related illness is a complicated process, one that’s not just about how the virus behaves, but how our immune response responds. Because so many people have been vaccinated or previously infected, it’s too early to tell if Omicron is naturally milder or simply stopped by this trained immune system before it can cause too much trouble.

A blunt attack

Speaking of immunity, there is still good and bad news on that front.

A preprint paper on BioRXiv this week, for example, compared how the Omicron variant responded to antibodies collected from previously infected people and those who had received different vaccines – not just the two mRNA vaccines from Moderna and Pfizer/BioNTech, but also the AstraZeneca vaccine, the Johnson & Johnson Injection , as well as vaccines from Russia and China. Across the board, compared to the parent virus and alpha variant, levels of neutralizing antibodies (the kind that help prevent infection) significantly decreased specific to Omicron. For both the Johnson & Johnson vaccine and Russia’s Sputnik V, levels dropped to the point where little protection against infection would be expected.

The results are consistent with other evidence indicating that vaccines are not good at preventing infection by Omicron. Recent data from South Africa, where the variant was first discovered, estimates that the effectiveness of the Pfizer vaccine in stopping infection dropped from 80% to 33% once Omicron became dominant.

At the same time, antibodies are not the complete picture of immunity. Studies released this week have suggested that T cells — another important line of defense against known germs — are specific to the coronavirus stay robust even in the face of Omicron, as many scientists expected. These cells are thought to very important to prevent the infection from causing serious illness. And while scientists are rapidly developing an Omicron-specific vaccine, booster shots based on the original virus appear to provide a buffer even there. A study by Moderna this week found that levels of neutralizing antibodies climbed noticeably backwards after a third shot.

Boosters were worth it before Omicron was in the mix, but they’re looking more cautious by the minute.

The Origin of Omicron

One of the many mysteries surrounding Omicron is where it came from. It was first discovered in South Africa in November, but that’s not necessarily where it comes from — the country’s impressive genetic surveillance may have spotted it before anyone else.

Aside from geography, there is also the issue of his origin. All variants of care to date have had only minor adjustments to their basic structure, but Omicron has: up of 30 mutations in its spike protein alone. Since scientists are now constantly monitoring the evolution of the coronavirus by periodically looking at the genetics of virus samples collected from patients, it would be very strange for a variant to pick up so many mutations right under our noses without notice – and yet, that’s exactly what seems to have happened here.

Currently, there are two main theories as to how Omicron came to be. One is that the variant originated in an immunocompromised person, where the infection could last much longer than normal and adapt to a weakened immune system, allowing some populations of the coronavirus with these mutations to survive and then be passed on to someone else. The other is that Omicron mutated while in an animal host and then jumped back to humans. a pre-print paper by scientists in China this week posits that Omicron’s ancestor jumped from humans to mice, and at some point later jumped right back to humans, now with a brand-new genetic set-up.

Based on their lab experiments, the researchers claim that the mutations found in Omicron aren’t very similar to the mutations we’ve seen before in human-hosted viruses, but they do resemble mutations seen in strains collected from mice. hosted cells. Omicron’s mutations are also somewhat similar to the mutations that may allow the virus to better infect mouse cells, they say.

Collectively, our results suggest that the precursor of Omicron jumped from humans to mice, rapidly accumulated mutations conducive to infecting that host, and then jumped back into humans, pointing to an interspecies evolutionary trajectory before the Omicron outbreak. , they wrote.

These are not the only scientists theorizing an animal origin for Omicron. And it’s certainly plausible – scientists have been Worried We’ve been talking about this kind of evolution for a while, as it became clear that the coronavirus could easily jump from humans to other animals. This is only preliminary work and more research will certainly be done. For context, there are still fierce debates about the origins of the pandemic itself two years later, so answers to Omicron’s source may not come easy either.

The arrival of Omicron should remind us that, as far as we can and have adapted to the virus, the germ can learn new tricks over time.

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